Construction of Spiro[indoline‐3,3′‐pyridazines] and Spiro[indene‐2,3′‐pyridazines] via TEMPO‐Mediated Oxidative Aza‐Diels‐Alder Reactions

A TEMPO promoted oxidative aza ‐Diels‐Alder reaction of ketohydrazones with 3‐methyleneoxindoles or 2‐arylidene‐1,3‐indanediones were successfully developed, This reaction provided an efficient synthetic protocol for novel functionalized spiro[indoline‐3,3′‐pyridazines] and spiro[indene‐2,3′‐pyridazines]. This reaction showed high diastereoselectivity and strict substituent's electron effect, which might be due to the reaction mechanisms process including sequential oxidative generation of 1,2‐diaza‐1,3‐dien and normal electron‐demand aza ‐Diels‐Alder reaction.